Build a system around speakers in the $5-$7.5K

I am currently rebuilding my system around my new Revel Studios. Great speaker especially used for around $7K.
which pushes your estimate envelope to the extreme.

I love these speakers. Great dynamics and soundstaging.
Great HF extension and very good LF extension. They look great to. (Well, they do to me, especially since we recently redecorated the living room in a more modern style.) Very revealing and accurate.

Make sure you leave yourself enough money to buy fairly powerful amp(s) though, as they are a bit power hungrey.
Sensitivity = 87db, and they dip down to an impedence of 3 ohms, although the average is 6 ohms, I believe. I use a 200W/ch Levinson amp (No. 23). It works very well with the speakers.

Other used speakers I would consider in the price range:

Sonus Faber Cremonas (Very good, lacks a little bass)

Wilson Sophia (Very good, similar to Studio, in a Wilson kind of way.)

The two new Quad electostatics (Sorry, I can't remember the numbers.)

This is a very subjective question. However, I personally would go on a natural and musicaly sounding system. MBL is ideal for both amplification and source, but you would better look for used equipment. Alternatives for the gear could be Plinius and MSB/Mark Levinson for the source.

Heard some GREAT new speakers at CES 2004 ... Vandersteen Quatros ... $6500 new.

I personally would purchase a used pair of Shahinian Diapasons. Like Roy said this is very subjective. Each of the best speakers available have tradeoffs. If you let us know what type of music you listen to and how important imaging, volume levels, deep bass and dynamics are then we can narrow your list. You will get many suggestions on this post. The following names however have repeatedly shown up in the magazines and Audiogon as speakers people love. (I'm sure I left a few out)
In No Particular Order
Vandersteen
Quad
Magneplanar
Wilson Audio
Avantgarde
Shahinian
MBL
Soundlab